1. Field of the Invention
The present invention relates generally to processing of plastic articles and, more particularly, to processes that provide enhanced reheating capability, as necessary, for article precursors such as preforms, and which form plastic articles that display enhanced handling characteristics.
2. Description of the Prior Art
Plastic articles, such as polyethylene terephthalate (PET) containers including bottles, are commonly formed in a one-step or two-step process. In the one-step method, a preform is typically injection molded and remains in a heated state as it is transferred to a blow mold where it is blown into the completed product. In the so-called two-step process, which is generally preferred for the manufacture of carbonated beverage bottles, the molded preform is first cooled and may be stored before it is transported to be reheated and blown into the final article at a later stage in the processing. As a result, in any two-step process, preforms must be reheated prior to blow mold processing. The requirement of reheating poses a problem in the two-step process.
Because PET is a notoriously poor heat conductor, the step of reheating preforms prior to blow molding is a lengthy and inefficient proposition which is compounded by the fact that preforms are relatively thick before they are stretched and blown into the formed article. A number of patents are directed to various apparatus for reheating preforms, most of which involve radiative heating, such as U.S. Pat. Nos. 5,326,258; 4,605,839; 4,476,364; 4,423,312; 4,396,816; 3,975,618; and Re. 34,177.
Another significant problem encountered in processing plastic articles, whether made by the one-step or two-step process, is that the ultimately formed article suffers from a "tacky" outer surface due at least in part to electrostatic forces. In this regard, as the blown articles exit the blow mold, the articles are typically conveyed to an accumulator in advance of a palletizing operation. In the accumulator, the articles are susceptible to static electric adhesion upon article-to-article contact. Production efficiency is inhibited because the articles must be manually separated from each other.
From the foregoing, it will be appreciated that there still exists a need in the art for processing plastic articles in a one-step or two-step process in which the bottles do not adhere to each other in an accumulator following the blow molding operation. There further exists a need in a two-step process in which preforms can be more efficiently reheated prior to entry into the blow mold.